This invention is directed to layered photoresponsive imaging devices which contain particular classes of disazo compounds. In one embodiment of the present invention there is provided a photoresponsive imaging member comprising a hole transport layer, and a photogenerating layer comprising various specific disazo compounds. These imaging members possess high photosensitivity, excellent panchromaticity, high cyclic stability, and other advantages illustrated herein. In addition, the imaging members are non-toxic and can be prepared by economical methods, thereby rendering them readily disposable. Also, the photoresponsive imaging members of the present invention are useful for various electrophotographic printing and imaging processes wherein latent images are formed on the imaging member, subsequently developed and transfered to a suitable substrate; and optionally permanently affixed thereto.
Xerographic photoconductive members are known, such as those consisting of a homogeneous layer of a single material including vitreous selenium, or composite layered devices containing a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive members is described in U.S. Pat. No. 3,121,006, which discloses finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. Imaging members prepared according to the teachings of this patent contain a binder layer with particles of zinc oxide uniformly dispersed therein, which layer is coated on a paper backing. The binders disclosed in this patent include materials such as polycarbonate resins, polyester resins, polyamide resins, and the like, which are incapable of transporting injected charge carriers generated by the photoconductive particles for any significant distance. Accordingly, the photoconductive particles must be in a substantially contiguous particle to particle contact throughout the layer for the purpose of permitting the charge dissipation required for a cyclic operation.
Photoreceptor materials comprising inorganic or organic materials wherein the charge generating and charge transport functions are accomplished by discrete contiguous layers are also known. Additionally, layered photoreceptor members are disclosed in the prior art, including photoreceptors having an overcoat layer of an electrically insulating polymeric material. Other layered photoresponsive devices have been disclosed, including those comprising separate photogenerating layers and charge transport layers as described in U.S. Pat. No. 4,265,990. Photoresponsive materials containing a hole injecting layer overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and a top coating of an insulating organic resin, are disclosed in U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of transport layers include certain aryl diamines as illustrated therein. The disclosures of U.S. Pat. Nos. 4,265,990 and 4,251,612 are totally incorporated herein by reference.
Many other patents exist that describe layered members containing photogenerating substances, such as U.S. Pat. No. 3,041,167, which discloses an overcoated imaging member containing a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. This member can be selected for electrophotographic imaging processes by initially charging the member with an electrostatic charge of a first polarity, followed by exposing it to form an electrostatic latent image that can subsequently be developed to form a visible image.
Also, there are disclosed in U.S. Pat. No. 3,574,181 disazo compounds useful as coloring agents. Several of the compounds represented by the structures disclosed at, for example, column 1, lines 25 to 72, are similar to those of Formula II of the present invention, however, the compounds of the '181 reference include halogen substituents on the central aromatic groups; and further this patent does not describe structures having halogen substituents in the specific positions detailed for the disazo compounds of the present invention. The identities and positions of the halogen substituents on the terminal aromatic groups of the disazo compounds of the present invention provide photoconductive imaging members having superior xerographic properties such as high photosensitivity, good dark development potential, low dark decay values, and excellent panchromaticity.
Composite electrophotographic photosensitive materials containing various azo compounds are disclosed in U.S. Pat. No. 4,618,672, wherein bisazo compounds particularly suitable for use in the charge generating layer of a layered electrophotographic photoconductor are illustrated. Included in the teachings of this patent is a compound of the structure shown at, for example, column 1, lines 9 to 27, that is similar to that of the Formula I compounds of the present invention, but with no dihalogenation of the terminal phenyl groups, whereas all the compounds of Formula I of the present invention possess dihalogenated terminal phenyl groups. Similarly, an article by M. Hashimoto entitled "Electrophotographic Sensitivity of Fluorenone Bisazo Pigments," Electrophotography, Vol. 25, No. 3 (1986), discloses disazo compounds similar to those of Formula I as charge generating materials in electrophotographic layered photoreceptors. This article discusses a relationship between the electronegativity of substituents on the disazo compound and electrophotographic sensitivity. The compounds discussed in this reference, however, do not possess the dihalogenated terminal phenyl groups found in all of the Formula I compounds. Japanese Patent Kokai No. 54-20736 discloses disazo pigments as constituents in electrophotographic processes. Many disazo compounds are disclosed in the aforementioned reference, including those at, for example, pages 215 and 216, that have formulae similar to that of the compounds of Formula II of the present invention although the terminal phenyl groups do not contain the same substituents in the same positions. Japanese Pat. No. 58-177955 discloses many disazo compounds suitable for use in the photosensitive layer of an electrophotographic device, including some that are somewhat similar to those of the present invention.
Further, U.S. Pat. No. 4,390,611 discloses an electrophotographic photosensitive member with a photosensitive layer containing an azo pigment selected from a large class of compounds. Some of these compounds, including those disclosed at, for example, column 3, lines 10 to 20 and 55 to 70; column 4, lines 30 to 53; and column 6, lines 47 to 58, are similar to those of Formula II although none include therein terminal phenyl groups with fluorine or chlorine substituents at the sites indicated in Formulae I and II. Additionally, U.S. Pat. No. 4,551,404 at column 2, column 3 at lines 45 and 60 to 68, and columns 4 and 5, bridging paragraph; U.S. Pat. No. 4,596,754 at column 6, lines 25 and 65, and column 9, lines 1 to 19; and Japanese Pat. No. 60-64354 at pages 402 and 403, disclose electrophotographic devices containing azo compounds which resemble those of the present invention. Several additional references illustrate layered organic electrophotographic photoconductor elements with azo, bisazo, and related compounds, such as U.S. Pat. Nos. 4,400,455; 4,390,608; 4,327,168, 4,299,896; 4,314,015; 4,486,522; 4,486,519; and Japanese Patent Publication No. 60-111247. None of these references, however, discloses photoreceptors formulated with the specific disazo compounds disclosed herein and possessing all of the advantages of the members of the present invention.
Copending application U.S. Ser. No. 851,051, the disclosure of which is totally incorporated herein by reference, describes photoconductive imaging members containing a supporting substrate, azo pigments as photogenerating materials, and a hole transport layer preferably containing an aryl diamine compound dispersed in an inactive resinous binder. Imaging members containing disazo compounds closely related to those selected for the present invention are disclosed on page 6, and in FIGS. 3-7, 3-8, and 3-9 of this application. Copending application U.S. Ser. No. 851,066, the disclosure of which is hereby totally incorporated by reference, also discloses photoconductive imaging members containing a supporting substrate, certain azo pigments as photogenerating materials, and a hole transport layer that preferably contains an aryl diamine compound dispersed in an inactive resinous binder. The azo pigments used as photogenerating materials in this copending application, however, differ significantly from the azo compounds selected as photogenerating materials for the present invention.
Although photoconductive imaging members with disazo compounds are known, including those very similar to the disazo compounds of the present invention, a need remains for disposable photoconductor devices. There also continues to be a need for layered photoresponsive imaging members containing azo compounds that will generate high quality images, even after repeated use in many imaging cycles, without succumbing to deterioration from the machine environment or surrounding conditions. In addition, a continuing need exists for improved layered photoresponsive imaging members wherein the azo compounds selected for one of the layers are substantially inert to the users of such members. Also, an important need exists for inexpensive layered azo photoconductors of high cyclic stability, high photosensitivity, good dark development potential, low dark decay, and high panchromaticity.